Disk drive with a pivot embedded torque generating track follow actuator and method therefor

ABSTRACT

A disk drive system (and method) includes an actuator system including a first voice coil motor (VCM), a second voice coil motor for enhancing dynamic resonance properties of the actuator system, and a single error position detecting mechanism, thereby enabling a higher bandwidth servo system configured with a single position error detection source.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention generally relates to a disk drive, and moreparticularly to a disk drive having a pivot embedded torque generatingtrack follow actuator.

[0003] 2. Description of the Related Art

[0004] Growth in areal density (bits/sq. inch) of a hard disk drive(HDD) is achieved through an increase in track density and bit densitymetrics. Technical advancement in electromechanical components and servosystem architecture facilitates the increase in track density.Indirectly, an increase in track density requires a commensurateincrease in crossover frequency of the track following servo transferfunction. A 3.5″ HDD for server class applications reached a trackdensity of 30 kTPI (tracks per inch) in year 2000, and the growth isexpected to continue into the next decade.

[0005] Actuator resonance modes have become fundamental limiters inachieving higher servo crossover frequency required for high TPI design.

[0006] The sector servo system of a 3.5″ server class HDD with a 1 kHzopenloop crossover frequency has been able to meet 30 kTPI (tracks perinch) track-following accuracy requirements. However, the growth oftrack density to higher than 30 kTPI has emerged as a major challenge tothe actuator and servo system design.

[0007] Further, mechanical system resonance is a key limiter to higherbandwidth control. Use of microelectromechanical (MEMs) devices has beenstudied to increase actuator response characteristics. A majorinnovation in the actuator system design to increase the servo crossoverfrequency is desirable, but the storage industry needs cost-effectiveinnovations in servo system design. A drastic change in the actuatorsystem design does not retain the time-proven simple actuator systemconcepts. Thus, an alternative servo-mechanics approach is required tomeet the high track density challenges. However, prior to the presentinvention, such an alternative, optimized approach has not beenpresented or developed.

[0008] For example, turning to FIGS. 1A-1B, a conventional rotaryactuator assembly 110 of a disk drive has a single voice coil motor(VCM) 120. It produces a force about a pivoting point in order togenerate a change in radial position of the read/write head.

[0009]FIG. 1A shows the conventional rotary actuator assembly 110 foundin a HDD. The actuator (and actuator arm 115) is made to pivot (e.g., bya pivot bearing assembly 150) about an axis when the VCM 120 isactivated. As shown the actuator assembly 110 further includes a pivotassembly body 130.

[0010] The pivot itself is composed of a pair of ball bearings 160A,160B, as shown in FIG. 1B, which are assembled with an appropriatepreload so that the pivoting function is made to be sufficiently free ofrotational stiffness. The ball bearings 160A, 160B, along with an innershaft 170, are fitted inside of a bearing sleeve or housing 180, withthe pivot assembly body 130 being fitted over the pivot bearing assembly150. Thus, the shaft and ball bearings support the entire actuatorassembly 110. The linear radial stiffness of the bearings 160A, 160B ishigh enough to maintain the resonance of a rigid actuator to be around10 kHz. In a “real world” application, the radial stiffness of thepivot-bearing contributes to general reduction of the free-bodyvibration of the actuator assembly 110. Early recognition of pivotstiffness induced dynamics as a detractor and a solution to it can befound in commonly-assigned U.S. Pat. No. 5,267,110, incorporated hereinby reference.

[0011] Recently several institutions have shown initiative in addressingthe problem of finite radial stiffness (e.g., see K. Aruga, “High-speedorthogonal power effect actuator for recording at over 10,000 TPI, IEEETransactions on Magnetics, Vol. 32, No. 3, May 1996).

[0012] Turning now to FIGS. 2A-2B, there are several actuator resonancemodes associated with a 3.5″ form factor HDD.

[0013]FIG. 2A shows a graph of magnitude with respect to frequency. Thatis, when a force (current) is applied to the actuator, the head isanticipated to move in a certain way (e.g., a certain frequency willresult in the conventional actuator arm assembly).

[0014] The first important mode (e.g., resonance peak) that occursaround 7 kHz is understood to arise from bending of the actuator voicecoil motor around its pivoting point. The coil bending resonance (CBR)is associated with a 180-degree phase change (e.g., see FIG. 2B whichshows the phase as a function of frequency) and in certainconfigurations the magnitude/phase combination could produce an unstablecondition of the track-follow servo. This bending mode characteristicalso is sensitive to temperature, pivot parameters and other designparameters of a disk drive.

[0015] Conventional approaches of managing the presence of this modehave been to introduce a digital notch filter in series with the servocontroller during a seek and track-follow mode. A notch filter reducesthe negative effect of the peak gain that occurs due to the coil bendingresonance (CBR). Because of the temperature-induced drift of theresonance frequency as well as the manufacturing variability encounteredwithin a population of a product, the digital notch filters are designedto have wider than required attenuation bandwidth, thereby resulting ina corresponding phase loss in the crossover region of the servo loop.The loss of phase in turn limits the achievable crossover frequency ofthe track-follow servo system.

[0016] Another industry effort to tackle the CBR has been to include anactive damping servo loop within the conventional positioning servo(e.g., see F. Huang, T. Semba, W. Imaino and F. Lee, “Active Damping inHDD Actuator,” Digests of APMRC2000,” ISBN 0-7803-6254-3, November 2000,page MB6-01). This method, which is theoretically equivalent to that ofan optimized digital notch filter, has been implemented in some serverclass HDDs.

[0017] A passive method to enhance the CBR resonance through structuralmodification is proposed in J. Heath, “Boosting servo bandwidth,”Digests of APMRC2000,” ISBN 0-7803-6254-3, November 2000, page MP20-01.Briefly, suppressing the CBR by various methods has a time limitedadvantage, and it does not allow for progressive growth in servocrossover frequency required for next generation HDDs.

[0018] Thus, the impact of coil resonance in the track-follow servotransfer function must be minimized, and hence requires new innovations.The present actuator system with a single VCM is primarily optimized forseek operation. The track-follow performance is extracted from the sameactuator structure as a secondary challenge. However, this constraintmust be removed in order to achieve not only an optimum access but alsoa high track density settle-out and track follow performance. H. Yamuraand K. Ono, “New H-infinity design for track-following,” Digests ofAPMRC2000,” ISBN 0-7803-6254-3, November 2000, page TA4-01 proposes aconfiguration in which the contribution of CBR is circumvented by asecond actuator.

[0019]FIG. 3 shows a conventional disk torque generating actuatorconcept in which a generic torque producing VCM configuration fortrack-following operation is suggested (e.g., see the above-mentionedU.S. Pat. No. 5,267,110, incorporated herein by reference).

[0020] In FIG. 3, the torque generator 300 includes a main VCM 310, apivot 320, a “mini-VCM” 325, a load-beam 330, and a head 340 whichprovides an input to a servo 350. The servo 350 also receives an inputfrom a rotation velocity sensor/servo 360 coupled to the main VCM 310.The servo 350 provides outputs to the main VCM 310 and the mini-VCM 325to move the head about the pivot.

[0021] It is noted that this system developed in that the previousconventional system employed only the main VCM. However, a problem arosein that, in applying a force to the arm (and thus the head) by the mainVCM 310 (e.g., based on a signal from the servo), a clockwise torqueshould result, thereby moving the head in a clockwise direction.

[0022] However, because of the configuration of the previousconventional device, in applying the force (and moving the head) tocreate a clockwise torque, a force was also being produced along thepivot normal axis 370 of the actuator (e.g., upward). The normal axis370 is orthogonal to the actuator long axis 380, as shown in FIG. 3. Dueto the compliance of the pivot 320, a linear motion was also beingproduced in the normal axis 370 direction of the entire system, therebymoving the head in a direction opposite to where the head was desired tomove (e.g., clockwise). Thus, the mini-VCM 325 was developed andprovided to apply an opposite force to ensure the head was compensatedfor and moved in the desired clockwise direction.

[0023] However, with the provision of the mini-VCM 325 and trying toavoid the problems occurring with the compliance of the pivot, spaceproblems have arose in the tight design space of the disk driveespecially with disk drive platters provided over the actuator armsclose to the pivot. Thus, these problems have made provision of a secondcoil unattractive in the conventional design.

[0024] Thus, the conventional systems have failed to produce an actuatorstructure that is capable of enhancing the track-follow performancewithout being constrained by the seek actuator design. However,realization of this concept in a product having disk platters (e.g., atight, small-space environment) and other components sensitive to anelectromagnetic field requires significant innovation.

[0025] Prior to the present invention, neither the advantages of such aconcept have been recognized, let alone a practical development of sucha concept even been undertaken. Indeed, there has been no system whichhas optimized the move/seek time for large displacements, compensatedfor the resonance features which appear as a result of thebearding/pivot compliance as well as the bending of the entire main-VCMstructure (e.g., a relatively large structure), and yet simultaneouslyprovided a compact system.

SUMMARY OF THE INVENTION

[0026] In view of the foregoing and other problems, drawbacks, anddisadvantages of the conventional methods and structures, an object ofthe present invention is to provide an actuator structure (and method)which is capable of enhancing the track-follow performance without beingconstrained by the seek actuator design.

[0027] Another object is to realize such a concept in a product havingdisk platters and other components sensitive to an electromagneticfield.

[0028] Another object is to provide a method and system which providescompensation for a relatively low frequency resonance (e.g., having apeak around 7 kHz, as shown in FIGS. 2A-2B) and which, at the same time,optimizes the move/seek time for large displacements.

[0029] In a first aspect of the present invention, a disk drive system,includes an actuator system including a first voice coil motor (VCM), asecond voice coil motor for enhancing dynamic resonance properties ofthe actuator system, and a single position error detecting mechanismcommonly provided for the first and second voice coil motors.

[0030] In a second aspect, an actuator assembly for a disk drive systemhaving a main voice coil motor (VCM), includes an actuator distributedto generate torque for track-following in addition to the main voicecoil motor.

[0031] In a third aspect, a computer system, includes a disk drivesystem, and an actuator assembly for the disk drive system having a mainvoice coil motor (VCM), and an actuator distributed to generate torquefor track-following in addition to the main voice coil motor.

[0032] In a fourth aspect, a pivot assembly for a disk drive systemhaving a main voice coil motor (VCM), includes a pivot member, and anactuator embedded in the pivot member to generate torque fortrack-following in addition to the main voice coil motor.

[0033] In a fifth aspect, a spindle assembly for a disk drive systemhaving a main voice coil motor (VCM), includes a spindle, and anactuator embedded in the spindle to generate torque for track-followingin addition to the main voice coil motor.

[0034] In a sixth aspect of the present invention, a servo systemassembly for a disk drive system, includes a first actuator, and asecond actuator having a smaller form factor than the first actuator togenerate torque for track-following in addition to the first actuator.

[0035] In a seventh aspect, a computer memory system, includes a diskdrive system, and a servo system assembly for the disk drive system, theservo system including a first actuator, and a second actuator having asmaller form factor than the first actuator to generate torque fortrack-following in addition to the first actuator.

[0036] In an eighth aspect of the present invention, a server system,includes an actuator system including a first voice coil motor (VCM),and a second voice coil motor for enhancing dynamic resonance propertiesof the actuator system.

[0037] In a ninth aspect of the present invention, a method ofgenerating torque for track following in a disk drive, includesproviding an actuator system including a first voice coil motor (VCM),and distributing a second VCM in the actuator system for enhancingdynamic resonance properties of the actuator system and for generatingtorque for track-following in addition to the first VCM.

[0038] With the unique and unobvious aspects of the present invention, asystem and method are provided in which an actuator structure enhancesthe track-follow performance without being constrained by the seekactuator design.

[0039] In this regard, the invention compensates for (e.g., negates) theeffect of the low frequency resonance and simultaneously provides apractical drop-in solution (e.g., a retrofit onto existing systems withminimal disruption and redesign of the existing systems). That is, insituations where the conventional actuator is not enough to provide therequired bandwidth (e.g., as track densities are increasing), theinventive actuator system can be “dropped in” in place of theconventional actuator, without demanding major changes in the way therest of the drive components are developed.

[0040] Hence, of the options available, the conventional systemoperators need not “gold plate” (e.g., fine-tune) the existing design ofthe systems, nor do they need to jump to an entirely new technology(e.g,. usage of MEMs, dual actuators, etc.). Instead, the systemoperators can use the invention as a “drop-in” solution, therebyproviding an integrated, proven system having great cost savings andminimal risk.

[0041] Additionally, all of the experiences of vendors of spindle motordesign can be easily leveraged into making the pivot VCM.

BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The foregoing and other purposes, aspects and advantages will bebetter understood from the following detailed description of preferredembodiments of the invention with reference to the drawings, in which:

[0043] FIGS. 1A-1B respectively illustrate a conventional disk actuatorassembly 110 and a pivot bearing assembly 150;

[0044] FIGS. 2A-2B illustrate a typical open-loop transfer function withthe actuator resonance modes;

[0045]FIG. 3 illustrates a conventional torque generating actuator 300;

[0046]FIG. 4 illustrates a pivot modified to generate torque using apivot-Voice Coil Motor (VCM) 450 according to the present invention incomparison to the conventional pivot bearing assembly 150 of FIG. 1B;

[0047] FIGS. 5A-5C illustrate a structure of the pivot embeddedpivot-VCM according to the present invention with a moving magnet/movingyoke configuration;

[0048] FIGS. 6A-6D illustrate a structure of the pivot embeddedpivot-VCM with a moving coil/moving yoke configuration according to thepresent invention;

[0049] FIGS. 7A-7B illustrate a computed track-follow transfer functionof the pivot-VCM of the invention as compared to the conventional VCMconfiguration;

[0050]FIG. 8A illustrates a torque generating parameters for seekoperation;

[0051]FIG. 8B illustrates a cross sectional parameters of the seekmagnet/yoke assembly;

[0052]FIG. 8C illustrates a coil geometry for the pivot-VCM of thepresent invention;

[0053]FIG. 8D illustrates a plan view of the coil/magnet/yoke assemblyof the pivot-VCM of the present invention;

[0054]FIG. 8E illustrates an equivalent magnetic circuit of thepivot-VCM of the present invention;

[0055]FIG. 8F illustrates a torque constant scaling of the pivot-VCM ofthe present invention;

[0056]FIG. 8G illustrates a coil resistance scaling of the pivot-VCM ofthe present invention;

[0057] FIGS. 9A-9B illustrate a structure of the pivot embeddedpivot-VCM with a moving coil/fixed yoke configuration, with FIG. 9Ashowing a top view of the pivot having a pivot-VCM coil and FIG. 9Bshowing a cross-section of the pivot including a bearing shaft and pivotVCM magnet/yoke;

[0058]FIG. 10 illustrates an arm embedded moving coil (vertical)/fixedyoke configuration of the pivot-VCM of the present invention;

[0059] FIGS. 11A-11B illustrate a horizontal pivot-VCM 1170 locatedbelow the rotating disk surface;

[0060] FIGS. 12A-12B illustrate a horizontal pivot-VCM 1270 locatedabove the rotating disk surface; and

[0061] FIGS. 13A-13B illustrate an alternative positioning of horizontalpivot-VCM 1370 from those shown in FIGS. 11A-12B.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

[0062] Referring now to the drawings, and more particularly to FIGS.4-13B, there are shown preferred embodiments of the method andstructures according to the present invention. It is noted that forconsistency and clarity the same reference numerals will be used throughthe application and drawings to designate the same structures.

[0063] Generally, the invention provides a configuration for a diskdrive position mechanism having multiple force generating actuators. Theactuators are optimally located to achieve both seek and settleout/track follow performance using a single position error source with asector servo architecture.

[0064] The invention belongs to a category of dynamic systems in which aSingle Output (position error) is controlled by Multiple Inputs (MISO).A practical realization of the configuration is made feasible byembedding the track-follow actuator system into the pivot assembly. Thisdesign innovation modularizes the development process of a disk drive bydecoupling the seek actuator/arm design from the pivot assembly design.Experience and expertise accrued from the design of compact spindlemotor design methods is deployed to achieve an effective pivot-VCM forhigh bandwidth track-following servo configuration. Variations in thedesign is made possible by allowing either the coil or the magnet to bemoveable. The track-following dynamic torque is shown to modify themagnitude and phase properties of the transfer function in aconstructive direction so that a higher band width servo system is madepossible.

PREFERRED EMBODIMENT

[0065] Turning now to FIG. 4, a preferred configuration is shown of thepresent invention in which the pivot element 150 of the conventionalactuator (e.g., as shown in FIG. 1) is modified to achieve a torquegenerating pivot-VCM configuration.

[0066] In the present invention, pivot shaft 470 that is attached to thebase plate of a HDD carries a pair of coils windings 475 at minimum sothat geometrically symmetrical and opposing force components can begenerated to produce a torque about the pivot shaft 470. Attached to thebearing sleeve 480 are magnets 485. The magnets 485 move along with themain body of the actuator arm assembly 110.

[0067] FIGS. 5A-5C show detailed views of a first configuration in whichthe moving magnet pivot assembly 450 (e.g., with the stationary coil) ofFIG. 4 is provided, with FIG. 5A showing a top cross-sectional view ofthe pivot bearing, FIG. 5B illustrating a shaft 470 with a coil 475Aattached thereto, and FIG. 5C illustrating a cross-sectional view of thepivot shaft 470 with first and second coils 475A, 475B. As shown, thecoil initially has a rectangular shape which is fitted to the shaft bycurling it to embrace the circular/cylindrical geometry of the shaft.The coils may be adhered to the shaft by epoxy or the like. It is notedthat, while only two pairs of coils (one on each side) are shown inFIGS. 5A-5C for generating a symmetrical torque, more than two pairs maybe provided (e.g., a four-pair system). Preferably, an even number offorce generators for generating an equal and opposite force, areprovided. As shown in FIG. 5A, the magnetic flux passes through thecenter shaft 470, through an air gap, through the moving bearing sleeve,back through the air gap, and back into the center shaft.

[0068] An advantage of this design is that the electrical links to thecoils 475A, 475B, are stationary, and they do not require delicateflexible cabling into a space constrained region of the actuatorassembly 110.

[0069] A disadvantage is that the magnet carrying bearing sleeve 480 issubject to a radial stress resulting from the magnetic potential field(magnetic flux) in the air gap, and the stress distribution can giverise to a residual torque that can affect the bias force requirement, orcan contribute to undesirable actuator dynamics following a seek. Thus,the magnetic flux exerts a radial stress on the bearing sleeve 480, andif there are imperfections in the four magnets, then a radial force maynot be perfectly controllable and the radial force may be non-zero.During a large seek, this non-zero radial force could undergo a force“ripple” effect which could excite some undesirable dynamics.

[0070] It is noted that, while some exemplary dimensions are provided inFIGS. 5C, for example, in FIG. 5C, the invention is in no way limited toor requires such dimensions. Indeed, the invention is scalable towhatever dimensions are desirable and/or being used by the industry overtime.

[0071] Further, it is noted that the invention could be assembled in anyof a number of ways depending upon the manufacturing requirements,constraints, and efficiencies. Indeed, the magnets could be put firstaffixed (via epoxy or the like) on a relatively thin stainless steelsheet member and that member could be inserted into to the sleevewithout the use of specialized processes. Moreover, the coils could beformed of copper wires or the like formed on a thin flexible circuitcable (e.g., 20 turns could be formed on each of five flex circuitcables and a multilayer structure could be formed via soldering the flexcircuit cables)

[0072] FIGS. 6A-6D show detailed cross-sectional views of an alternativepivot-VCM configuration in which the embedded pivot-VCM includes theflux in the sleeve, with FIG. 6A showing a top view of the pivot in theactuator arm assembly, FIG. 6B illustrates a cross-section of the pivotbearing, FIG. 6C illustrates a detailed view of the magnetic coils onthe sleeve, and FIG. 6D illustrating a top view of the pivot bearing.

[0073] That is, in this case, the air gap flux is produced by stationarymagnets 685 and the current carrying coil windings 675 are attached tothe bearing sleeve 480. Also shown in FIG. 6B are ball bearings 690supporting the moving coil 675 and a bearing shaft 695. A drive cover691 and a drive base plate 692 are also provided, as well as a coil-wireexit 693.

[0074] The disadvantage of this design is that the electrical linkageshould be provided by a flexible circuit. The challenge of radial stressremains the same as the bearing sleeve 480 is still required to carrythe air gap flux.

[0075] That is, the possibility of the ripple effect is still present inthis alternative configuration. The inertia due to moving coil isarguably smaller than that of a moving magnet configuration. However,due to proximity to the pivot center, the difference in the incrementalinertia of the pivot-VCM pivot may not be substantial.

[0076] Further, in the design of FIGS. 6A-6D, since the flux of themagnets must pass through the center shaft, the center shaft preferablyis made thinner than in the case of the shaft of FIGS. 5A-5C. Otherwise,the flux may be actuated too soon.

[0077] FIGS. 7A-7B show an estimated track-follow dynamics of thepivot-embedded VCM as opposed to the conventional VCM.

[0078] It can be observed in FIG. 7A that the gain peaking at 7 kHz isreduced by about 20 dB (e.g., a factor of 10), and, as shown in FIG. 7B,the phase change is no longer a 180-degree lag (as in the conventionalVCM) but is only a positive lead (a localized phase change). The firstcalculated 180-degree phase lag occurs just above 15 kHz.

[0079] Thus, as shown, the design approach has merit in enhancing thedynamic performance by an embedded pivot-VCM. Hence, with the invention,the stabilizing phase is reduced significantly with the invention andallows the system to behave even under the effects of resonance (exceptfor minor local variations). That is, the invention cuts down on theresonance participation in the VCM (e.g., the resonance mode in anegative way into the servo system behavior)

[0080] FIGS. 8A-8G show an exemplary torque generating capability of apivot-VCM as extrapolated from a conventional actuator design, and thescalability of the pivot-VCM torque motor. Once again, the dimensionsshown are for exemplary purposes only and are in no way for limiting thepresent invention.

[0081]FIG. 8A shows the geometric and electromagnetic parameters,whereas FIG. 8B shows the magnetic circuit parameters of a conventional3.5″ form factor seek VCM. Similarly FIGS. 8C-8E show the parameters ofa pivot embedded VCM.

[0082]FIGS. 8F and 8G show how the scaling would impact the torque andresistance factors. It can be observed from FIG. 8F that a torqueconstant k which is 10% of the conventional torque constant can berealistically achieved. On the other hand, the resistance is expected tobe about 4 times higher than that of a conventional VCM. Since thecurrent requirements are expected to be about 100 mA RMS, for a 5 to 12V operation, the increase of resistance by 4 times can be easilymanaged. Thus, as shown, the invention can be easily scaled to existingconventional designs (and indeed scaled to even smaller designs) toprovide the drop-in solution as mentioned above.

[0083] FIGS. 9A-9B show a radially expanded pivot design having a coil975 arrangement and where the air gap flux is returned not by thebearing sleeve but by a U-cross sectional yoke 980 held by the baseplate 692. That is, the base plate area 692 is shown for locating thestationary magnet assembly, and the pivot embedded pivot-VCM is shownwith flux in the external yoke 980.

[0084] This moving coil design, as shown in FIG. 9A, includes threecylindrical members including the outer bearing sleeve 480 for carryingthe main VCM actuator arm, an intermediate cylindrical member 981 forcarrying the moving pivot coil 975, and an inner cylindrical member 982for carrying the shaft/ball bearing arrangement.

[0085] This design eliminates radial stress on the bearing sleeve (if itis made of non-ferromagnetic material). Further, this design has moretorque generating capability and yet is still integrated with the pivotdesign. However, a disadvantage of this design is that it requires alarger body housing (e.g., larger diameter) on the actuator since thedesign positions one more flux carrying member into the gap.

[0086] Thus, in the moving coil design of FIGS. 9A-9B, the magnetic fluxis carried to the metallic yoke by two flux carrying portions (twostationary yokes) that are inserted into the system design. The coilitself is preferably supported by a non-ferromagnetic material, so it“sees” no magnetic force.

[0087]FIG. 10 shows the design concept 1000 of FIGS. 9A-9B of anembedded pivot-VCM, but applied as an independent design from that ofthe pivot. Therefore, this design would be useful where the conventionalpivot is desired as it is, or where the arm assembly is built by avendor (OEM) forming the arm initially (e.g., not a retrofit), and twoslots already exist on the arm (e.g., one for the pivot and one for thepivot-VCM), thereby allowing the arm to carry the pivot-VCM design.Thus, an advantage of this design is that there is more flexibility indesign as there is more space to manipulate the design. Further, puretorque is being generated by the vertical design (e.g., verticallyembedded coil). Hence, the full height of the actuator is being used toadvantage with this design.

[0088] Additionally, with the inventive design, now that the pivot-VCMcoil is available during seek, some additional force could be applied bythe pivot-VCM to assist the main-VCM during a seek. This would allow themain-VCM to become smaller, if desired by the designer.

[0089] However, the modularity of actuator design and pivot design iscompromised in this embodiment, and further the arm weight becomeslarger, thereby resulting in either the arm moving slower or a higherpower being required to move the arm. Further, as the configurationbecomes larger, there is a higher likelihood of the resonances fallingback down.

[0090] Turning now to the details of FIG. 10, a slot 1010 is formed inthe actuator arm for the pivot-VCM and magnet yoke assembly also showsthe electrical connection (e.g., line 1020) requirement where thefeedback from servo controller 1030 from the microprocessor and currentdrivers is provided through a system flexible cable 1040 that usuallycarries the read/write information and main VCM current. Further,electrical pins 1050 are shown for connection to the flex cableconnector.

[0091] FIGS. 11A-11B and 12A-12B show another configuration where thetorque producing pivot-VCM pairs are configured in a horizontal plane(i.e., a plane parallel to the disk platters).

[0092] That is, FIGS. 11A-11B show a case where the coils 1170 (e.g.,flat, horizontal coils as opposed to vertical coils) are placed belowthe bottom disk-platter 1110 supported by a motor spindle 1120. Thus,the pivot-VCM is positioned at the bottom of the actuator arm 1115. FIG.11A is a cross-sectional view of the pivot VCM, whereas FIG. 11B is atop view showing the dual pivot-VCM 1170 on both sides of the actuator1115. Further shown are the magnets and yoke assemblies 1130.

[0093] FIGS. 12A-12B show a case where the coils 1270 are placed abovethe uppermost platter. FIG. 12A is a cross-sectional view of the pivotVCM, whereas FIG. 12B is a top view showing the dual pivot-VCM 1270 onboth sides of the actuator arm 1215. It is noted that the top disk 1210of the disk platters has been removed for clarity. Also shown are themotor spindle 1220 and the yoke/magnet assemblies 1230.

[0094] A concern in the design of FIGS. 12A-12B is the magnetic leakage.Further, the mechanical resonance advantage that a pivot integratedbearing could produce is somewhat diminished because of the slenderdesign of the horizontal pivot-VCMs.

[0095] It is noted that, notwithstanding the configuration of thedesigns of FIGS. 11A-12B, the coils can be placed advantageously inpositions different from the top or the bottom of the actuator arm. Thatis, as track densities increase, consumers will not necessarily requireor desire as many disk platters on the same spindle.

[0096] Thus, it is envisioned that, in disk drives, the number ofplatters will decrease (e.g., possibly reduced from the current six diskplatters down to one or two disks). Hence, with the reduction of thenumber of disks, there will be greater flexibility in the positioning ofthe coil and thus, for example the coil could be placed in the centerbetween two disks.

[0097] Hence, a pivot VCM could be positioned, for example, in aposition intermediate the top and bottom of the actuator arm. Indeed,the coils could be placed in the middle of the actuator arm.

[0098] FIGS. 13A-13B show a case where the coils 1370 are placed betweenthe uppermost platter and the lowermost platter. FIG. 13A is across-sectional view of the pivot VCM, whereas FIG. 13B is a top viewshowing the dual pivot-VCM 1370 on both sides of the actuator arm 1315.It is noted that the middle disk 1310 of the disk platters has beenremoved for clarity and shielding (unreferenced) has been provided. Alsoshown are the motor spindle 1320 and the yoke/magnet assemblies 1330.

[0099] Additionally, it is noted that a plurality of coils need not beprovided regardless of the position desired (e.g., top, bottom, ormiddle). That is, a single coil (moving or stationary) could be used, asshown in FIGS. 13A-13B.

[0100] With the unique and unobvious aspects of the invention, anactuator structure (and method) is provided which enhances thetrack-follow performance without being constrained by the seek actuatordesign. The invention also provides a method and system for compensatingfor a relatively low frequency resonance and which, at the same time,optimizes the move/seek time for large displacements, and provides apractical drop-in solution with minimal disruption and redesign of theexisting systems.

[0101] While the invention has been described in terms of severalpreferred embodiments, those skilled in the art will recognize that theinvention can be practiced with modification within the spirit and scopeof the appended claims.

[0102] For example, the invention can be employed in computer systems,server system using computer memory systems such as high performancecache systems, and the like. For example, in server systems employingcache memory applications, two drive systems can be used employing thestructure of the present invention. Hence, in a server system, insteadof providing a plurality of expensive disk drives, low-access data maybe placed on a low-cost drive and higher access data may be placed onmore costly drive.

What is claimed is:
 1. A disk drive system, comprising: an actuatorsystem including a first voice coil motor (VCM); a second voice coilmotor for enhancing dynamic resonance properties of the actuator system;and a single position error detecting mechanism commonly provided forsaid first and second voice coil motors.
 2. The disk drive system ofclaim 1, wherein said first VCM comprises a large form factor actuatorand said second VCM comprises a compact form factor actuator.
 3. Thedisk drive system of claim 1, further comprising a pivot for receivingsaid second VCM.
 4. The disk drive system of claim 1, further comprisingan actuator arm for receiving said second VCM.
 5. The disk drive systemof claim 1, wherein said second actuator is modular.
 6. The disk drivesystem of claim 1, wherein each of the first and second voice coilmotors receives a single position error signal from said single positionerror detecting mechanism.
 7. The disk drive system of claim 1, whereinthe single position error detecting mechanism provides an input to aservo controller commonly provided for said first and second voice coilmotors.
 8. An actuator assembly for a disk drive system having a mainvoice coil motor (VCM), comprising: an actuator distributed to generatetorque for track-following in addition to said main voice coil motor. 9.The actuator assembly of claim 8, wherein said disk drive system furtherincludes a pivot, and wherein a plurality of actuators are provided,wherein said plurality of actuators are embedded into the pivot formodularity and ease of assembly.
 10. The actuator assembly of claim 8,wherein said plurality of actuators include “n” coils for enhancing atorque generating capacity of said plurality of actuators such that anet force is zero and a net torque is cumulative.
 11. The actuatorassembly of claim 10, wherein said coils each comprise a flat coil. 12.The actuator assembly of claim 10, wherein said coils are provided inpairs such that each coil of said pair participate in the forcegeneration process.
 13. The actuator assembly of claim 10, wherein “n”is an even number.
 14. The actuator assembly of claim 10, furthercomprising a mechanism for moving said coils.
 15. The actuator assemblyof claim 10, wherein said coils comprise movable coils.
 16. The actuatorassembly of claim 10, further comprising a plurality of movable magnets.17. The actuator assembly of claim 16, wherein said coils arestationary.
 18. The actuator assembly of claim 10, wherein said diskdrive further includes a main actuator body, said actuator includes apivot-voice coil motor (VCM) embedded into said main actuator body. 19.The actuator assembly of claim 18, wherein said pivot-VCM includes forcegenerating members distributed parallel to the pivot axis.
 20. Theactuator assembly of claim 18, wherein said pivot-VCM includes forcegenerating members distributed in a plane normal to the pivot axis. 21.The actuator assembly of claim 18, wherein said pivot-VCM is positionedin an uppermost portion of said main actuator body.
 22. The actuatorassembly of claim 20, wherein said pivot-VCM is positioned in anuppermost portion of said main actuator body.
 23. The actuator assemblyof claim 18, wherein said pivot-VCM is positioned in a lowermost portionof said main actuator body.
 24. The actuator assembly of claim 20,wherein said pivot-VCM is positioned in a lowermost portion of said mainactuator body.
 25. The actuator assembly of claim 24, wherein saidpivot-VCM is further positioned in an uppermost portion of said mainactuator body.
 26. The actuator assembly of claim 18, wherein saidpivot-VCM is positioned in an intermediate portion of said main actuatorarm.
 27. The actuator assembly of claim 26, wherein a coil of saidpivot-VCM is positioned between first and second disk platters situatedin said disk drive system.
 28. The actuator assembly of claim 20,wherein said pivot-VCM is positioned in an intermediate portion of saidmain actuator arm.
 29. A computer system, comprising: a disk drivesystem; and an actuator assembly for the disk drive system having a mainvoice coil motor (VCM), and an actuator distributed to generate torquefor track-following in addition to said main voice coil motor.
 30. Apivot assembly for a disk drive system having a main voice coil motor(VCM), comprising: a pivot member; and an actuator embedded in saidpivot member to generate torque for track-following in addition to saidmain voice coil motor.
 31. A spindle assembly for a disk drive systemhaving a main voice coil motor (VCM), comprising: a spindle; and anactuator embedded in said spindle to generate torque for track-followingin addition to said main voice coil motor.
 32. A servo system assemblyfor a disk drive system, comprising: a first actuator; and a secondactuator having a smaller form factor than said first actuator togenerate torque for track-following in addition to said first actuator.33. A computer memory system, comprising: a disk drive system; and aservo system assembly for the disk drive system, said servo systemincluding: a first actuator; and a second actuator having a smaller formfactor than said first actuator to generate torque for track-followingin addition to said first actuator.
 34. The computer memory system ofclaim 33, wherein said computer memory comprises a cache memory.
 35. Aserver system, comprising: an actuator system including a first voicecoil motor (VCM); and a second voice coil motor for enhancing dynamicresonance properties of the actuator system.
 36. A method of generatingtorque for track following in a disk drive, comprising: providing anactuator system including a first voice coil motor (VCM); anddistributing a second VCM in said actuator system for enhancing dynamicresonance properties of the actuator system and for generating torquefor track-following in addition to said first VCM.
 37. The method ofclaim 36, wherein said first VCM comprises a large form factor actuatorand said second VCM comprises a compact form factor actuator.
 38. Themethod of claim 36, further comprising providing a pivot for receivingsaid second VCM.
 39. The method of claim 36, further comprisingproviding an actuator arm for receiving said second VCM.
 40. The methodof claim 36, wherein said second actuator is modular.